Fabricating a plastic stormwater chamber

ABSTRACT

A method of making a molded plastic arch shape cross section stormwater chamber having a corrugated wall comprises molding half chambers which are connected by hinges at a joint at the top of the chamber. The chambers may be compactly stored and transported in splayed out configuration. Later, upward force is applied to the hinge joint location of each chamber, so the half chambers are rotated by force of gravity, whereby a faying surface on each half chamber is urged toward the like surface of the other half chamber. The faying surfaces are then fused to each other, preferably as a result of prior heating or by melting of a fusion weld element that is captured in the space between the faying surfaces.

This application is a continuation-in-part of application Ser. No.14/025,773, filed Sep. 12, 2013, now U.S. Pat. No. 9,233,775, issuedJan. 12, 2016.

TECHNICAL FIELD

The present invention relates to methods of making molded plasticchambers having arch shape cross sections, particularly large chambersfor receiving, holding and dispersing water when buried beneath thesurface of the earth.

BACKGROUND

Arch shape cross section storm chambers made from injection moldedplastic have been used for a number of years to handle stormwater. In atypical installation, multiple rows of strings of interconnectedchambers are placed on the floor of a cavity made in the earth surfaceand are then backfilled with crushed stone or the like. Stormwater, suchas might run-off from a paved parking lot or roofs of buildings ischanneled to the chambers so the waters can accumulate and then bedispersed over time by either percolation into the surrounding soil orby controllably flowing to a water course.

Some types of arch shape cross section chambers, exemplified by acorrugated chamber described in DeTuillo U.S. Pat. No. 5,087,151, haveclosed ends and are interconnected by pipes. Those chambers might bemade by thermoforming of thermoplastic sheet. Another type of chamber,of more relevance to the invention described herein, is exemplified bythe chambers shown in Kruger U.S. Pat. No. 7,118,306. Those kinds ofchambers are preferably made by injection molding. The chambers haveopen ends. A string of chambers is assembled by overlapping a first endof one chamber on the second end of a like chamber, when the likechamber has been previously placed within a cavity in the earth. Afterinstallation, the chambers are backfilled, typically with crushed stone,and the stone is covered to create a soil surface, often a paved surfacewhich can be used by motor vehicles. When so installed beneath thesurface of the earth, stormwater chambers should have requisite strengthand durability, particularly for bearing the overlying load of soil andany vehicular or other traffic.

Systems comprised of molded plastic arch shape cross section stormwaterchambers are in functional- and cost-competition with other stormwatersystems, including buried systems comprised of steel conduit anddetention ponds. Generally, it is an objective to have storm chamberswith larger and larger volumetric capacity per unit length, while ofcourse still meeting the load bearing requirements. Whereas earlyplastic chambers used 20 years or more ago had a peak height of 12inches, more recent chambers may be quite large. For example, acommercial Model 4500 stormwater chamber sold by Stormtech LLC, RockyHill, Conn. is 100 inches (2.54 m) wide at the base, about 60 inches(1.52 m) high, about 48 inches (1.22 m) long, and weighs about 120pounds (55 kilograms). There is a generalized desire to commercializeeven larger chambers.

There are practical problems encountered with making and handling largechambers. Among them are:

First, it is not easy to mold large chambers because they require largemolding machines and machinery for handling the just-molded products.Large and thus less common injection molding machines can be costly.

Second, large chambers present problems with respect to storing and toshipping in economic fashion by truck—the most common mode. Typicallychambers are nested one within the other to form a stack for shipment onpallet. But when the height of a chamber is large to begin with, thenthat means not many chambers can be nested before the height capacity ofa ordinary highway truck is exceeded. For example, if the load heightcapacity of a truck is about 100 inches (254 cm) from the bed surface,and one chamber is 60 inches (152 cm) high, then there is only an about40 inches (102 cm) of space for containing nested chambers. If the stackheight is about 6 inches (15 cm) (the spacing between one chamber andnext-nested chamber), then only 6-7 chambers can be stacked on top ofthe bottom chamber.

The issue of shipping chambers efficiently has been addressed in thepast. In particular U.S. Pat. Nos. 4,245,924 and 4,360,042 of Fouss etal. describe an arch shape cross section conduit which has amolded-material hinge joint at the top. The corrugated side walls arefoldable inwardly to the point that the opposing side base flanges meetat the lengthwise vertical center plane of the conduit. The conduit isshipped in such flattened condition. At the point of use, the baseflanges are spread apart until a plastic fabric which connects the baseflanges becomes taut and stops further movement. Generally, roundconduits of the nature of corrugated pipe, which have so-called livinghinges (thin foldable regions) are known. See U.S. Pat. No. 6,364,575 ofBradley et al. for an example.

SUMMARY

An object of the invention is to provide large stormwater chambers whichhave improved characteristics with respect to manufacturability,shipment and handling. A further object is to provide a means for makingchambers comprising mated half chambers.

In accord with an embodiment of the invention, a molded plastic archshape cross section stormwater chamber having a corrugated wallcomprises separately molded half chambers which are connected by hingejoint at the top of the chamber. Preferably, the half chambers aresubstantially identical and are made in the same mold. Methods ofmolding the chambers enable providing a larger or smaller corrugation atone end of a chamber made from substantially identical half chambers.

Preferably, a chamber comprises two half chambers interconnected byhinge parts at the top of the chamber. Exemplary chambers assembled atthe factory can be stored and shipped in splayed out in nominal 180degree chord angle orientation; the arch flattened out and the baseflanges widely separated. Storage and shipping costs are reduced sincechambers can be stacked in splayed or flat condition. At a destination,typically near the point of use, a chamber can be lifted from the top ofa stack of splayed chambers resting on a pallet by pulling upward in thevicinity of the top joint (which alternately may be characterized aspulling upward in proximity to the top joint), whereupon gravity willcause the half chambers to rotate relative to each other about thehinges, so the chamber articulates to the arch shape cross section whichcharacterizes the use configuration, similar to a like chamber made inone piece.

In an embodiment of a method got putting mated half chambers into useconfiguration, mating surfaces (also called faying surfaces) proximatethe top of the chamber are fusion welded to each other. Preferably afusion weld element is captured between the mating surfaces at the topof the chamber and is caused to melt by means of electric resistanceheating or electromagnetic induction heating while the hinged-togetherhalf chambers are thrust upwardly at the hinge location. When a chamberis lifted (or thrusted) upwardly, the weight of each half chamber causesthe joint between the half chambers to close as the fusion weld elementmelts. In a preferred embodiment, the fusion weld process time andcurrent are controlled, repeatedly to produce substantially identicalchambers.

The foregoing and other objects, features and advantages of the presentinvention will become more apparent from the following description ofpreferred embodiments and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically shows in end view two identical half chambersclosely spaced apart from each other ready for mating at a lengthwisehinge joint. Each chamber having an imaginary chord A, B. FIGS. 1, 2, 3and 4 represent sequential configurations of a chamber.

FIG. 2 shows the half chambers of FIG. 1 in joined-together condition,also called the engagement configuration. Angle M between the chords A,B is greater than 180 degrees.

FIG. 3 shows the joined-together half chambers lying on a pallet. AngleM is 180 about degrees.

FIG. 4 shows the joined together half chambers suspended from a tetherat the top hinge joint. Angle M is acute.

FIG. 5 is a perspective view of a chamber comprised of half chambersjoined-together at a top hinge joint.

FIG. 6 is a view like FIG. 5, showing a locking rod lengthwise inexploded fashion, for locking together mated half chambers so they willnot splay apart.

FIG. 7 is a perspective view showing a stack of two splayed chambersresting on a pallet with a third chamber just having been lifted fromthe stack by a tether attached to the joint region.

FIG. 8 is a perspective view showing an alternate embodiment for liftinga chamber from the stack of FIG. 7, wherein the chamber maintains itssplayed shape during lifting.

FIG. 9 is a perspective view looking down onto a half chamber, showinghinge and joint features.

FIG. 10 is a close-up view of the joint at the top of a half chamberlike that shown in FIG. 9.

FIG. 10A is a schematic end view showing how stirrup plates at the topof half chambers mate during rotation of the half chambers about the tophinge joint.

FIG. 10B is a fragmentary end view related to FIG. 10A, showing matedstirrup plates in their home or rest position, when the chamber has anarch shape cross section.

FIG. 10C is a perspective view of the joint portion of a half chamber,showing a vertical flange and associated stirrup plate, along withpyramidal shape dowels.

FIG. 11 is a perspective view looking down onto the top of two halfchambers, showing how the hinge parts are configured to engage whenthere is lengthwise relative motion.

FIG. 12 is a close up view of one of what is shown in FIG. 11.

FIG. 13 is an end perspective view looking up into the concavity of ahalf chamber which has a lengthwise L shape top flange with serrations.

FIG. 13A is a perspective view of two mated half chambers like thoseshown in FIG. 13, along with an associated serrated C shape channel.

FIG. 13B is a perspective view of the portions of mated L shape topflanges of the half chambers of FIG. 13A, showing how the serrated Cshape channel engages serrated portions of the L shape top flanges.

FIG. 14 is an end perspective view of the half chambers shown in FIG.13A, showing a serrated C shape channel in place, to hold the chambersfrom hingedly moving apart.

FIG. 15 is an end perspective view of a portion of the top of a hingedjoint chamber, showing a latch at the end of the chamber.

FIG. 16 is a horizontal plane cross section through the latch locationof the chamber portion shown in FIG. 15.

FIG. 17 is a transverse vertical cross section view through the valleyportion of a chamber comprised of two hinge-connected half chambers,showing a latch in the valley.

FIG. 18 is a perspective view of the top portion of a half chamber alongwith associated clamps (in exploded position) which hold vertical plateportions of the half chamber to the corresponding portions of anidentical chamber.

FIG. 19 is a transverse vertical cross section view of the joint regionof a chamber comprised of two mated half chambers like the half chamberof FIG. 18, along with a clamp in its use-position.

FIG. 20 is a lengthwise cross section through the wall a half chamberprecursor, illustrating how alternate ends of the precursor are severedto produce first and second half chambers which mate with each other toform a chamber having a larger peak corrugation at one end.

FIG. 21 is a cross section through an injection mold cavity showing how,by inhibiting plastic flow to a portion of the mold, a half chamber maybe made which has a standard corrugation at one end and a largercorrugation at the other end.

FIG. 22 is a cross section through a mold having movable inserts at eachend of a mold cavity.

FIG. 23 is a detail view of one end of the mold shown in FIG. 22.

FIG. 24 is a partial schematic cross section of an end of a first halfchamber made in the mold of FIG. 22, along with a phantom of theopposite end of a like half chamber.

FIG. 25 is a partial schematic cross section of the end of a second halfchamber made in the mold of FIG. 22, after the mold inserts have beenre-positioned.

FIG. 26 is a perspective view of the top portion of a portion of halfchamber, where the joint surface has a fusion weld element tack-weldedto it.

FIG. 27 is a vertical cross section of the top of the half chamber ofFIG. 26, with a mated phantom half chamber, and with an upward-thrustingforce H.

FIG. 28 is a vertical cross section like that of FIG. 27 showing thewelded joint of two half chambers.

FIG. 29 is a more detail view of the joint shown in FIG. 28.

FIG. 30 is a view like FIG. 29, shown an alternative embodiment jointformed by hot plate welding, where the top half chambers have stops tolimit closure of the joint.

DESCRIPTION

Stormwater chambers and their use have been described in the art. Inparticular, reference may be made to commonly owned U.S. Pat. No.7,118,306 of Kruger et al., entitled “Stormwater Management System” andU.S. Pat. No. 6,991,734 of Smith et al, entitled “Solids Retention inStormwater System.” The disclosures of the foregoing patents are herebyincorporated by reference.

In the generality of the invention, an arch shape curve cross sectionchamber is comprised of two mating half chambers which are made byinjection molding of a thermoplastic such as polyethylene orpolypropylene, typically with a wall thickness of about 0.2 inches. Achamber embodiment of the present invention is characterized by a hingedlengthwise joint at the top of the chamber. A preferred hinged joint inthe present invention is distinguished from a so-called living hinge,wherein half chambers are integrally connected by a thin web ofmaterial, as in the Fouss et al. patents mentioned in the Background.Each half chamber is molded separately and then mated with the otherhalf chamber to form a whole chamber. In embodiments of the presentinvention, lengthwise motion of the half chambers relative to each otherenables making and unmaking of the joint therebetween.

FIG. 5 shows chamber 20, an embodiment of the present invention. Chamber20 has opposing sidewalls 23, 25 which together define an arch shapedcross-section and interior concavity of the chamber. Chamber 20 iscomprised of half chamber 22A and identical half chamber 22B. The topportions of the half chambers are connected to each other at lengthwisejoint 30 at the top of the chamber. Alternating peak corrugations 34 andvalley corrugations 32 (also called simply “peak” and “valleys”) runtransverse to the length axis L of the chamber within the sidewalls,from each base flange 28 to the top of the chamber. Joint 30 lies alongthe lengthwise vertical center plane which contains vertical axis CP andlength axis L. The top portions of each chamber are characterized byspaced apart ribs 26 that run transversely to the length of the chamberfrom the concave underside of each half chamber sidewall to a verticallengthwise stirrup plate 40 which plate is on or closely proximate tothe lengthwise vertical center plane of the chamber.

FIGS. 1-4 are simplified end views of half chambers which illustratesome basic aspects of the present invention. FIGS. 1-4 are to beconsidered sequentially. For purposes of description here, each halfchamber 22A, 22B has an imaginary line A, B (hereafter referred to asthe chord) which runs from the inner edge of the base flange 28 to thatpart of the half chamber which is in the vicinity of the top of the halfchamber (which alternately may be characterized as being in proximity tothe top joint) and which contacts a flat surface, when the half chamberis placed on the flat surface with its interior concavity facing theflat surface. In the simplified embodiment of FIG. 1-4, that contact ismade at the lower edge of rib 26. Chords A, B are also shown in FIG. 5.

FIG. 1 shows two half chambers 22A and 22B after molding and before theyare connected to each other. As illustrated by FIG. 2, the joint 30 ismade by hinge assemblies 24. (In FIGS. 1-4 and some other view, thehinge parts 24 are shown in simplified fashion. Mating hinge parts 36,38 which function as hinge assemblies 24 are described in more detailbelow, for example, in connection with FIG. 9.) Preferably, the hingeparts 24 may be longitudinally engaged and disengaged from each otheronly when angle M between the chords A, B is significantly greater than180 degrees, i.e., 10-20 or more degrees greater. As will be appreciatedfrom the details below, when the preferred half chambers are pivotedrelative to each other at the hinge points, so that the angle betweenthe chords is significantly less than 180 degrees, the mated hinge partscannot disengage from each other.

FIG. 3 shows the joined-together half chambers 22A, 22B lying in splayedout fashion on a pallet 44, ready for shipment. Angle M is nominally 180degrees.

FIG. 4 illustrates what happens when a chamber 20 is lifted verticallyfrom the pallet by pulling upwardly in vicinity of the joint 30, thatis, generally at the top of the chamber, by such as a strap H shown inphantom. The half chambers 22A, 22B rotate relative to each other sothat angle M becomes an acute angle, i.e. less than 180 degrees. Ribs 26and associated elements (for example, vertical stirrup plates 40 orsubstitutional plain flanges, described below) on one half chambercontact corresponding plates/flanges on the other half chamber, andthereby limit how small angle M can become. That limiting smallest valueof angle M is chosen so that the bottoms of the base flanges 28 lieparallel to each other in the base plane BP. In this condition, theinterior concavity of the chamber, that is the cross section, is archshaped, as illustrated in FIG. 5, and the chamber is suited forplacement at its use location, typically in a cavity in the earth.

In FIG. 4 and FIG. 5, chamber 20 is in what is called here its useconfiguration, as distinguished from its transport configuration shownin FIG. 3 or as distinguished from an in-between configuration. Chamber20 has a height ha in its use configuration which is much lesser thanthe height hc it has in its transport configuration. For example hc isonly about 40-50 percent of ha. Thus it will be appreciated that abouttwice as many nested chambers can be contained within a given stackheight on a pallet when the chambers are splayed as shown in FIG. 3,assuming the stack height of nesting (the vertical distance betweencorresponding features of stacked items) is nominally the same in bothconditions. Thus the economic and practical advantage of the inventionfor reducing cost of storing and shipping chambers will be appreciated,as more chambers can be fit into a given space.

FIG. 7 is a somewhat less schematic illustration of what is shown inFIGS. 3 and 4. FIG. 7 shows two splayed out chambers 20 resting on apallet 44 shown in phantom, while another chamber 20A is being raised upby a schematically shown lifting strap H that is attached to the chambertop. When a chamber is lifted from its splayed transport position on apallet, by lifting in vicinity of its top joint, gravity will cause theangle M to decrease until interference at joint parts prevents furtherdecrease. As described below, this method of lifting it advantageouswhen each half chamber is welded to the other at joint 30.

While a preferred way of lifting a chamber 20 from a pallet is thatwhich was described in connection with FIG. 7 and FIG. 4, alternativemodes of lifting may be used. For example, FIG. 8 shows a lifting strapHH with leaders 44 running to three points on the chamber 20; thechamber is being lifted from the stack while preventing gravity-inducedpivoting of the half chambers relative to each other. After the chamber20 is placed on the ground nearby, it can then be lifted at the centerjoint by a strap or by manual lifting, or it can be otherwisemanipulated to cause it to assume the desired arch shape cross sectionshown in FIG. 5. The FIG. 8 alternative mode of lifting requires lessclearance space above a pallet of stacked splayed-out chambers than doesthe mode of FIG. 7. Of course, another way of removing a chamber from astack or pallet is for workers manually to lift it by the edges.

The manner in which hinge assembly 24 can be engaged and disengaged (ifever desired) is of particular advantage in the manufacturing andtransporting process of the present invention. In a preferred embodimentof the method invention, a first half chamber 22A is injection moldedfirst, removed from the mold, and laid on the pallet 44. Then anidentical second half chamber 22B is injection molded in the same mold,removed from the mold, and then moved through space to proximity to thefirst half chamber 22A, as by an industrial robot. The second halfchamber is hingedly engaged with the first half chamber using techniquessuch as those described below. During the hinge-engagement, the halfchambers are oriented to each other as shown in FIG. 2; that is, theincluded angle between the chords is greater than 180 degrees, and thusthe mating hinge parts of the two half chambers can be mated to at amultiplicity of hinge assemblies 24 spaced apart along the length of thetop of the chamber. In a preferred embodiment, to accomplish the hingeengagement, the second half chamber 22B is moved lengthwise relative tothe static half chamber 22A, or vice versa. After the hinges areengaged, half chamber 22B is rotated downwardly onto the surface of thepallet to a position like that shown in FIG. 3 and FIG. 7, whereupon thehinges cannot be disengaged; and, the chamber is ready for storage,shipment and later lifting when that is desired.

Mating the half chambers shortly after removal from the molding machineprovides an unexpected advantage in that good fit and easy engagement,in particular at the hinge parts, is assured. Experience shows that theshrinkage, or dimensional change of a molded part upon cooling or withtime after cooling, can vary from part to part within a run, or amongstparts from one run compared to parts from another run. When the partsare large, as are half chamber embodiments of the present invention, thedimensional changes can be large enough in an absolute sense adverselyto affect the fit between half chambers, to the extent they might notengage.

FIG. 9-12 illustrate features to the joint which is formed betweenembodiments of half chambers. FIG. 9 is a perspective view looking downat the top of a single half chamber 22A which is representative of thetwo identical half chambers 22A, 22B. For clarity, FIG. 9 is asimplified view in that strengthening panels 52 described in connectionwith FIG. 11-12 are omitted and there are no individual stirrup plates;there is only a vertical flange 45 at the top of the half chamber. Theexterior surface of the top of half chamber 22A is characterized byhinge parts 36, 38 that are located within valleys 32. There are twokinds of hinges: essentially male hinge parts 38, e.g., comprisingpintles 46 as shown in FIG. 10C, and essentially female hinge parts 36,e.g., comprising gudgeons 50 as shown in FIG. 12. The gudgeons areshaped to receive the pintles. Preferably hinge parts 38 alternate withparts 36 along the length of the half chamber top which forms half ofthe joint in a whole chamber.

FIG. 11 shows how a joint is formed between two closely positioned halfchambers. The two half chambers are shown in a position where they areready to be moved lengthwise relative to each other so the hinge parts36, 38 mate. FIG. 12 is an expanded view of what is shown in FIG. 11; itshows in more detail the longitudinally engageable hinge parts. FIGS. 11and 12 show how pintle 46 of hinge part 38 is shaped to enter thegudgeon 50 of hinge part 36 when the half chambers 22A, 22B are placedin close proximity and when the half chamber 22B is moved lengthwise, asindicated by the arrow T in FIG. 11.

Pintle 46 of hinge part 38 preferably has an integrallengthwise-extending key 48 on its exterior. See FIG. 12. The key isshaped to enter the slot 54 associated with gudgeon 50. When key 48passes through the slot 54 of hinge part 36, and half chamber 22B (andthus hinge part 36) is rotated relative to half chamber 22A (and thusrelative to hinge part 38), pintle 46 is captured lengthwise withingudgeon 50 because key 48 prevents disengagement so long as the key isnot aligned with slot 54.

Thus, from the foregoing it will be understood why, as described abovefor FIGS. 1-4, the half chambers can be engaged with each other when ina particular greater-than-180 degree angle M chord orientation, namely,because the key 48 and slot 54 are aligned in that position. When thehalf chambers are rotated about the hinge connection so the angle Mnears 180 degrees or is less than 180 degrees, the half chambers cannotdisengage from each other because the keys of the pintles do not line upwith the slots of the gudgeons. As an example, the hinge parts may beengaged and disengaged other only when the angle between the chords isabout 210 degrees. In the generality of the invention, other go/no-goangles M may be chosen, for example to address a circumstance where thechambers are stacked in other than flat (180 degree chord angle M)position, such as being stacked with angle M of 150 degrees. Tore-articulate generally the foregoing construction of chamber comprisedof half chambers and its features: There is a critical value X of angleM between the chords of the half chambers. (In the foregoing examples,X=150 degrees and X=180 degrees.) When angle M is greater than X, thechambers are longitudinally engageable and disengageable at the hingeparts. When angle M is less than X, the chambers cannot be engaged ordisengaged.

Other means than a key may be used to limit engagement-disengagement toa particular angle M. For example, the pintle may have an outer endwhich is irregularly shaped with portions that are larger than thediameter of the rest of the pintle, and the gudgeon opening may fit thatirregular shape.

In another embodiment, the means for preventing relative lengthwisemotion of mated half chambers can be unassociated with the hinge itself.For instance, a tab can project from one half chamber in vicinity of thejoint, remote from the hinge, to engage a feature on the mating halfchamber when the chord angle is about 180 degrees or less, or to engageat all angles. For example, a latch of the type described below inconnection with FIG. 15 can be used to limit lengthwise motion. In stillanother embodiment of the invention, there is no means for limitingdisengagement; rather care is taken during handling not to move the halfchambers lengthwise.

In the generality of the invention, half chambers may be hingedlyconnected to each other without a construction which dictates a criticalgo no-go angle M. Lengthwise-motion locking means for pintle andgudgeons may be employed. For example a pin may be put into adiametrical hole at the end of pintle 46 after the half chambers aremated; a snap-ring may be placed within a groove formed at the outer endof pintle 46, and so forth. A pintle may be given an arrow shaped head,the base of which is slightly larger than the opening of the gudgeon; sowhen the head is resiliently forced through the opening, the reversemotion is prevented in the absence of great force or a special tool. Incarrying out the invention, separately formed hinge parts made of metal,plastic, or other material may be molded-into one or both half chambers,or attached to a half chamber after molding, as by means of fasteners orwelding.

In the generality of embodiments of the present invention, the termhinge (and variants) encompasses any kind of mechanical connectionbetween the top portions of the half chambers that enables relativepivoting of the half chambers in the transverse vertical plane of thechamber. A hinge in embodiments of the present invention does notprovide continuous material connection between the chambers, as does aliving hinge.

FIGS. 10, 10A, 10B, and 10C illustrate other features of the joint atthe top of a chamber 20, namely stirrup plates 40. Stirrup plates 40 aresubstantially vertical lengthwise structures which are attached to upperend of a half chamber corrugated sidewall and to ribs 26 which run invalleys, transversely on the concave interior surface of the halfchamber sidewall. As shown in FIG. 9, each stirrup plate 40 has aplurality of essentially semi-circular cylindrical arches or stirrups 41which run parallel to the half chamber length axis and are spaced apartfrom each other by slots 43. Slots 43 of one half chamber are shaped toreceive the stirrups 41 of the mating half chamber. While the stirrupplate 40 illustrated in FIG. 10 and FIG. 10 C is continuous along thelength of the half chamber, in an alternative embodiment a multiplicityof smaller stirrup plates are spaced apart along the length of thejoint.

FIG. 10A is a schematic end view illustrates the rotational matingmotion of stirrup plates 40 of one half chamber with the stirrup plates140 of an identical half chambers, as one stirrup plate 140 is beingrotated about hinge axis PP, as indicated by the arrow, to approach theanother.

FIG. 10B shows the plates 40, 140 as they have completed the rotationshown in FIG. 10A, thus reflecting their respective orientations whentwo half chambers are in the chamber use configuration. The plates 40,140 cannot go further toward each other than is shown in FIG. 10Bbecause vertical running portions of the plates, away from the stirrupsand slots, contact each other. When a chamber is in its useconfiguration, the mated semi-cylindrical arches (stirrups) of thestirrup plates 40, 140 define a lengthwise passageway 61. The pluralityof passageways 61 align with preferred 60 in the ribs 26 at the ends ofthe chambers. As illustrated in FIG. 6, a locking rod 42 is slidablelengthwise through holes 60 and passageways 61, to effect locking of themated plates 40 and to prevent the half chambers from separating.

When a chamber 20 is vertically loaded during use, as by the weight ofoverlying crushed stone or earth or pavement, etc., a bending moment canarise in vicinity of joint 30. One effect would be to separate the plate40 on one half chamber from the plate 140 on the mated half chamber,i.e., the joint could tend to open and the top could be prone to movedownward. Such a tendency is resisted by the engagement of plates 40,140 with locking rod 42.

FIGS. 10C, 11 and 12 show a half chamber embodiment 22B having verticalplates 52 at the upper ends of the valleys 32. This compares with theFIG. 9 half chamber embodiment 22A, where there are no plates. A plate52 can be characterized as vertical upward extension of a stirrup plate.Or plates 52 can be characterized as a top flange when there are nostirrups. Plates 52 connect adjacent peak corrugations 34 for furtherjoint strength. The presence of plate portions 52 also provides astructure to which may be attached the vertically extending portions ofhinges parts 36, 38. More strength and stiffness is provided to achamber.

FIG. 10C and FIG. 12 show optional pyramidal dowels 55 which projectoutwardly from the ends of peak corrugations 34. Dowels 55 are receivedin cavities 57 which comprise the underside of peak corrugations of themating half chamber. See FIG. 12. Not shown in portion of the exemplaryhalf chamber pictured in FIG. 10C is that the half chamber 22B has atotal of four peak corrugations 34. The other two peak corrugationswhich are not shown have no dowels; rather at those other peakcorrugations there is an opening 57 in the plate 40. Thus, whenidentical half chambers are mated and rotated to form the desired archshape cross section of the chamber in its use configuration, each dowelis aligned with, and is received within, an opening 57 in the plate 40,which opening 57 is to the half chamber concave interior and whichopening underlies the peak corrugation on the mating half chamber.Dowels 55 and associated receiving-cavities 57 can provide furtherstrength to the joint. In an alternative embodiment chamber, dowelspresent in pairs as just described.

In other embodiments of the invention, different means than stirrupplates and rods can be employed to lock together and or strengthen thejoint. An example is illustrated in FIGS. 13, 13A, 13B and 14. FIG. 13shows half chamber 122B having base flange 128 and a top flange 70Bwhich is L-shape in the vertical cross section plane of the chamber.

FIG. 13A shows two identical chambers 122B and 122A (each having arespective L-shape flange 70B, 70A) which a mated as part of top joint130. C shape cross section channel 74, a clamp, is shown in proximity tothe joint. In one embodiment, shown in FIG. 19 and discussed below, thehorizontal flange portions 72A, 72B are continuous and the clamp 74slides onto them by moving lengthwise. Portions of the preferredembodiment of FIG. 13A are shown in more detail in FIG. 13B. FIG. 14shows the clamp in its final use position. The horizontal portion 72B oftypical L-shape flange 70B is comprised of spaced apart cutouts 75. Inanother way of looking at it, the horizontal portion comprises spacedapart tabs 73. Clamp 74 has cutouts 76 which, when aligned with the tabs73 of the flange, enable the clamp to be moved vertically so the tabsare contained within the concavity of the clamp. Clamp 74 may then bemoved lengthwise along the chamber for a distance nominally equal to thelength of one tab. That results in the clamp being captured on the Lshape flanges, and opening of the joint at the hinge point is inhibited.Some bending moment resistance will be imparted.

In another embodiment of the invention, other features are used to holdthe half chambers together at the joint so they can be handled, and toallow installation of other securing means such as a locking rod 60 or aclamp 74. FIG. 15 and FIG. 16 show a portion of the end of ahinged-joint chamber 220 which comprises mated half chambers 222A and222B. A latch 78 engages a match plate 79, and holds the joint 230together. Latch 78 is shown as a hinged or swinging arm; a latch with aliving hinge or spring action may alternately be used. A hook and loopfabric latch may be used.

Still other substitutional mechanisms for holding the joint together,with like function and effect to those described above, may be used.FIG. 17 is a partial vertical cross section of chamber 320 having hingeconnection 324 and top joint 320. Mating plates 352A, 352B close theends of valleys 332A, 332B. Tab 388, which extends from valley 332B ofhalf chamber 322B, passes through slot 386 in the plates, when the halfchambers are pivoted about hinge point 324, to put the chamber in theuse configuration. The arrow shape head 388 and elastic action of thebody of the tab act to hold the plates together, and thus to keep thejoint closed.

The perspective view of FIG. 18 and the related vertical cross sectionview of FIG. 19 show still another embodiment of means for holding thejoint of mated half chambers together. Half chamber 422A mates halfchamber 422B at joint 430 as illustrated in the chamber fragment shownin FIG. 19. FIG. 18 shows one half chamber 422A. An identical matinghalf chamber is omitted from FIG. 19 for clarity, but can be imagined.Flange 452B runs lengthwise along the top end of typical half chamber422A. Flange 452B has vertical lip portions 492 which extend into theinterior concavities of the peak corrugations 434. The lip portions 492,when mated with the corresponding lip portions of a like chamber, areengaged by resilient-material clamps such as clamp 494, shown inexploded position in FIG. 18. In like fashion, flange 452B also has adownward extending portions 490 which, when mated with the correspondingportions of a like half chamber, as shown in FIG. 19, is engaged by Cshape clamp 494. As shown in FIG. 19, a portion 490 preferably is Lshape, comprising a ridge 495. And, clamp 494 is C shape, to engage theridge, to help hold the clamp in place. Like ridges may characterize thelips 492 and associated clamps 496.

In still other embodiments of chambers of the present invention, screws,bolt fasteners or welding, may be used in addition to or in combinationwith one or more of the features described here, to hold hinged halfchambers together. See the features of a welded and bolted joint,including joint interlocking and strengthening features described inrelated commonly owned U.S. Pat. No. 9,016,979 issued Apr. 28, 2015 andentitled “Plastic stormwater chamber made from separately molded halfchambers. The disclosure of said patent is hereby incorporated byreference.

Preferably, the half chambers are identical, as has been described. Inanother embodiment of the invention, one half chamber may be differentfrom the other half chamber. For example, the hinge parts on a firstkind of half chamber can be all of the male (pintle) type and the hingeparts on the second kind of half chamber can be all of the female(gudgeon) type. However, that eliminates an advantage of using the samemold for both parts; and it may be necessary to accumulate and keep onhand an inventory of first kind of half chambers, to await the change ofmold required to manufacture the second kind of half chambers. Theaforementioned advantage of avoiding shrinkage problems will be lost.

From the foregoing description of half chambers and resultant wholechambers, it will be appreciated that, by example, if there is atransverse projection at the joint at a first end of a half chamber,that same half chamber has to have a cavity at the other end to receivethe projection when two hinged half chambers are placed in the useconfiguration. Thus, along the length of a half chamber there cannot besymmetry about the mid point of the length of the half chamber.

However, using one mold to make mating identical half chambers presentsa problem with respect to how to enable a familiar kind of overlapconnection between chambers when they are connected end-to-end to form astring of chambers. In a typical prior art one piece chamber there is acorrugation at one end which is smaller (or larger) than the corrugationon the other end of the chamber. Thus, one chamber, oriented correctly,can overlap, or be overlapped by, another identical chamber.

But when a whole chamber is comprised of two mated identical halfchambers that have been formed in exactly the same mold, then thecorrugation at one end of a half chamber cannot be smaller than thecorrugation at the other chamber end. The reason is that when a halfchamber is rotated in space relative to the other half chamber, to makethe joint between two half chambers, any smaller or larger dimensioncorrugation at the first end of a first half chamber will align with,and not mate dimensionally with, a standard size corrugation at thesecond end of the mated identical half chamber.

The compliant nature of plastics means that in one embodiment of theinvention an overlap joint might be made between chambers of the presentinvention which have the same dimension corrugations at each end. Thecorrugation at the end of one chamber is laid upon the identical shapecorrugation at the end of the mating identical chamber. However, somecan see that as an imperfect joint because of the interference-fit atthe joint, owing to the effect of the wall thickness of the chamber.

Methods for manufacturing by injection molding mating half chambers willnow be described which address the foregoing problem. While themanufacturing methods are described in connection with half chambersused in constructing a hinged chamber of the present article invention,the methods may also be used for the chambers of the aforementionedcommonly owned U.S. Pat. No. 9,016,979 and potentially for otherarticles which have corrugations.

A first embodiment and second embodiment of the method invention isdescribed. In each a half chamber precursor is molded, and is then cutto make a half chamber. The first embodiment is illustrated in FIG. 20which shows the cross section of a half chamber precursor 320, asmolded, looking into a lengthwise plane, e.g., adjacent the jointregion. In the center portion of the part 320 are peak corrugations 82and valley corrugations 84 which have what is called here standard size.At each end of the chamber are peak corrugations 86A, 86B which arelarger than the standard size corrugations, sufficient to overlap astandard size corrugation. The nature of the overlap by peak corrugation86B of the end of portion of phantom chamber 88P having standard sizecorrugations is illustrated at the right side of FIG. 20.

Cut lines E and F are shown in FIG. 20. To make a first kind of halfchamber, a first precursor 320 is cut at line F, thereby to produce afirst half chamber having a length LC and a large peak corrugation 86Aat the left end, as shown in the Figure. Next, a second precursor 320 ismolded and it is cut at line E, to thereby produce a second half chamberalso having length LC and a large peak corrugation 86B at the right endof the half chamber, i.e., the opposite end of the first half chamberwhich was fabricated by cutting. The cut portions are discarded. Thus,when the first and second half chambers are rotated in space and matedto make a joint, the two larger peak corrugations 86A, 86B mate witheach other; and, the resultant chamber has a large corrugation at oneend, suited to overlap the standard corrugations at the other end of alike chamber, which other end comprises what were the cut-ends of theprecursors.

The second embodiment is illustrated by FIG. 21 which is a cross sectionthrough an almost schematic two part injection mold comprised of upperpart 90 and lower part 92. The mold is shaped to make a chamber part 97(which illustrated by only a single line for simplicity). The mold hasend portions B and C, connected by center portion A. The mold endportions B and C are shaped respectively to form a corrugation 94B, 94Cwhich is larger than the standard size peak corrugations 94 which areformed by the center portion A of the mold.

A phantom standard corrugation 94P is shown at the right of FIG. 21, toshow how it may be overlapped by a large corrugation 94B. To make afirst half chamber, the flow of plastic to mold portion C is shut offduring molding. Known appropriate kinds of shut-offs and flow controldevices for injection molding are used. Thus, a first half chamberhaving a length LC and a large peak corrugation 94B at one end, formedby portion B, is produced. Next, a second half part is formed byshutting off flow of plastic to mold portion B during injection molding.That results in a second half chamber which also has a length LC, butnow with a large peak corrugation 94C at one end, being the opposite endfrom that of the first half chamber having peak corrugation 94B. Thus,the first and second half chambers can be mated at a lengthwise joint attheir tops and to form a chamber having a large peak corrugationcomprised of mated features 94B and 94C at one end, while the other endof the chamber (and the middle) has a standard size corrugationcomprised of mated peak corrugations 94.

In a third embodiment of method for making chambers suited foroverlapping, there are moving parts within the injection mold. After afirst part is made, the internal parts of the mold are re-positioned sothe size of the second part has corrugations at each end which aredifferent from those of the first part. This is illustrated by FIG.22-24. FIG. 22 is a schematic cross section of a portion of an injectionmold having interconnected cavities which define a corrugated halfchamber. The mold is configured to produce a half chamber which hasstandard corrugations along the preponderance of the chamber length, anda smaller peak corrugation at one end. At each end of the mold crosssection are mold subassemblies 99L and 99R which contain moveableinserts. Each insert moves from a first position F to a second positionG. The movement takes place in the interval between a first injectionmold shot which forms a first half chamber and a second shot which formsa second half chamber.

In the first shot, the inserts, e.g., inserts 98A, 98B of subassembly99R, will be at position G and the inserts of the other subassembly 99Lwill be at position F. In the second shot, inserts of subassembly 99Lwill be at position F and inserts of subassembly 99R will be at positionG. The result will be that a first half chamber will be formed with asmall peak corrugation at one end (that defined by cavity 102L ofsubassembly 99L), and a second half chamber will be formed with a smallpeak corrugation at the opposite end from that of the first chamber,that defined by cavity 102R of subassembly 99R. Each chamber will havestandard peak corrugations along the rest of the length of the chamber.Thus, when the two different half chambers are mated, the smallercorrugations mate with each other and provide a chamber having astandard peak corrugation at one end and a smaller peak corrugation atthe other end.

In further explanation: FIG. 23 is a detail view of the portion of themold having subassembly 99R; it is typical of the subassembly 99L inFIG. 22. The mold comprises two mold parts 96A, 96B which defineinterconnected mold cavities 102L, 100M and 102L. Contained within themated mold parts is subassembly 99R, the moveable inserts 98B, 98A ofwhich define mold cavity 102R. (At the other end of the mold,subassembly 99L has corresponding parts and defines cavity 102L.) Theinserts of the two subassemblies 99L, 99R are movable in the verticaldirection, under action of unshown but conventional actuation means, incoordination with each other, and in simultaneous opposite directions.The inserts move from a first position F to second position G asindicated by the small arrows in FIG. 23. The inserts define mold cavity100R. The cavity 102R which the inserts 98A, 98B define is connected tothe middle cavity 102M at point 104R.

The first shot, with the slide assembly 99R in position F as shown inFIG. 23, and the slide assembly 99L in position G, produces a part 106like that shown in FIG. 24. The major part of the half chamber hasstandard corrugations 100, while the end corrugation 102 which wasformed in the slide assembly 99R is smaller. There is a jog at point 104where the corrugation 102 connects to the rest of the half chamber. InFIG. 24 the end of the half chamber which is opposite to the end 102 ofa like half chamber, namely chamber 106P, is shown in phantom, toillustrate how its standard size corrugations overlie the end 102.

For the next shot, the slide 99R is then moved to position G and theinserts of subassembly 99L are moved to position F. Plastic is injectedinto the mold to form a second half chamber which will have an end 102shaped like that shown in FIG. 25. There is now no jog at connectionpoint 104. The opposite end (not shown) will have a small corrugationdefined by mold cavity 102L.

Thus, when the first and second half chambers are mated at their topjoint, the small peak corrugations of the first and second half chambersmatch with each other and the standard corrugations at the other endsmatch each other. Thus an arch shape cross section chamber having afirst end which can be overlapped by the corrugation at the other end isformed.

All of the foregoing three embodiments may be carried out in alternativefashion by (a) substituting a valley corrugation for a peak corrugationat the end of the half chamber and chamber; or (b) making the sense ofthe end corrugation opposite to what has been described, i.e.,substituting a larger corrugation for a smaller corrugation or viceversa.

The following describes how a chamber may preferably be formed by fusionwelding in vicinity of the hinge joint between mated half chambers: afusion weld element is caused to melt by means of electric resistanceheating or electromagnetic induction heating. The melting takes placewhile the hinged-together half chambers are being thrusted or pulledupwardly in vicinity of the hinge location, so they move from a splayedout configuration to a use configuration, as illustrated by FIG. 7. Asdescribed previously, the weight of each half chamber (force of gravity)causes the hinge joint to close. Thus, when a fusion weld element whichis captured in the joint melts, the half chambers will rotate a smallamount relative to each other, to deform the element and more fullyclose the joint. In this portion of the description, the mating surfacesproximate the tops of the half chambers are sometimes referred to asfaying surfaces.

A preferred method of welding by using an electrically heated weldelement captured within the joint is described in commonly owned patentapplication Ser. No. 14/809,124 of R. Moore and P. Holbrook, filed Jul.24, 2015, entitled “Plastic tank having fusion welded parts” (the “'124application”), now U.S. Pat. No. 9,840,040. The disclosure of saidapplication is hereby incorporated by reference. The preferred method ofusing a fusion weld element is particularly useful when half chambersare permanently fastened to each other at a location remote from theoriginal manufacturing facility. In the generality of thismethod-of-forming invention, other means for welding may be used. Forinstance, familiar welding by use of hot air and filler rod, or hotplate welding, may be used.

A fusion weld element as the term is used here refers to a componentwhich can be heated by electrical or electromagnetic energy, sufficientto cause localized melting and fusion of both the element and the localplastic material of the parts being joined. Exemplary fusion weldelements comprise plastic with embedded metal pieces that are heated byelectric resistance or electromagnetic induction are described furtherbelow. Some commercial products are described below.

Placement of a fusion weld element may be accomplished in differentways. For example, the fusion weld element may be molded into thematerial of the half chamber when it is formed, as suggested byillustration in the related '124 application. Alternately, the elementmay be placed partly or wholly within in a groove on one of the fayingsurfaces; alternately, the element may be simply captured between thefaying faces as they are pressed toward each other. Preferably, in thepresent invention, the latter technique is used and a fusion weldelement is plastic-tack welded to a faying surface. As the fayingsurfaces are moved toward each other, the fusion weld element is raisedin temperature sufficient to melt the fusion weld element and localportions of the mating plastic surfaces. The application of electricenergy is then ceased and the weld zone is allowed to cool. Theresultant solid weld joint is fused plastic which weld-joins the twoparts. Some metal artifact from the metal portion of the fusion weldelement may remain within the fused plastic weld material. A fusion weldelement may be placed on one of the faying surfaces, alternately anelement may be placed on each faying surface.

FIG. 26 is a perspective view of the top portion of a lengthwise portionof half chamber 522A. Half chamber 522A is generally like half chamber22A that is shown in FIG. 9. The corrugated half chamber has peaks 534alternating with valleys 532. A smaller peak corrugation 534A is at theend of the chamber for better overlap of the end corrugation of a likechamber. A combination of female hinge elements (pintles) 536 and malehinge elements (gudgeons) 538 extend from tops of the peaks. Theelements 536, 538 are shaped to mate male-female with the like elementsof a mating half chamber. The joint surface 540A, which is also thefaying surface with respect to welding, has a fusion weld elementrunning along the surface. The fusion weld element generally follows thepeak and valley contour of the upper edge of the faying surface of thehalf chamber, and the contour of the lower edge of the faying surface.Alternative fusion weld element paths may be used. The terminal ends 81Tof a resistance heated type of fusion weld element extend from the jointat the end of the chamber (not shown) so they may be connected to anelectric power supply. While FIG. 26 shows one continuous faying surface540A and a fusion weld element that predominately runs lengthwise withrespect to the chamber length, in other embodiments of the inventionthere may be a multiplicity of spaced apart faying surfaces with anintegral weld element running between them, or with separate weldelements associated with each.

FIG. 27 is a vertical cross section through half chamber 522A, showinghow the fusion weld element 81 lies on the surface 540A, beingplastic-tack welded to the surface. In an alternative embodiment, twoparallel spaced apart fusion weld elements will run along the path ofthe single element shown in FIG. 27. That may be accomplished byproviding a U-shape element prior to the tack welding step. The fusionweld element is preferably tack welded to the faying surface before thehinged-together chamber is shipped from the factory, that is, aftermolding or after the half chambers are mated for putting on a shippingpallet.

FIG. 27 also shows in phantom a mating half chamber 528B, and by dashedarrow H, shows how an upward force is applied to the tops of the halfchambers at the joint location. The upward force may be applied eitherby means of a lanyard as shown in FIG. 7, or by means of a fixture whichpushes upwardly from beneath the chamber, or by up-thrusting orrotational forces applied to the base flanges, or by other logical meanswithin the ordinary skill. Preferably, the upward force is applied tothe hinge joint region and force of gravity will cause the half chambersto rotate toward each other as indicated by the arrows CM. As the upwardforce is applied, the faying surfaces of the two half chambers are urgedto approach each other, and as they do the weld element 81 is heatedsufficient to melt. The result is that the faying surfaces becomeattached to each other at the weld element location. The fusion processmight take 10 or more minutes. The electric power to the fusion weldelement is then terminated and the weld region is allowed toconductively and convectively cool.

FIG. 28 is a cross section through the top portion of a chamber at thesame location as shown in FIG. 27, which chamber has been formed in theforegoing fashion. Weld zones 83 at the top and bottom of the jointattach the half chambers 522A, 522B to each other. An advantage of theforegoing process as applied to hinged chambers is the avoidance ofcostly welding fixtures.

FIG. 29 is a more detail view of the joint 530. It will be appreciatedthat the regions on the faying surfaces 540A, 540B where there was nofusion weld element, are slightly spaced apart from each other at a gap587 by the weld elements 83 which have fused to both faying surfaces.The amount and duration of electric current that is applied to thefusion weld element is carefully controlled, based on experiment thatshows what is necessary to obtain a good weld. Thus, there is areproducible small spacing between the faying surfaces away from theweld element location. And that provides a reproducible configuration ofchamber when welding a multiplicity of chambers. If desired,tooling/fixtures or integral stops may be used to ensure the desiredfinal configuration of joint and chamber.

As mentioned above other welding techniques including flat plate weldingmight be used when hinged-together half chambers are lifted by a force Hto close the joint. A flat plate heating element may be inserted in thejoint prior to lifting at the hinge point, then removed, followed bylifting of the half chambers to form the weld joint. Optionally, duringthe heating/melting step there is a first lifting with the hot platecaptured in the joint for possible better heating. FIG. 30 is a crosssection like FIG. 29 showing how faying surfaces 640A, 640B are fused byweld 683 at joint 630 after the faying surfaces have been melted by ahot plate. Stops 85A, 85B which extend from the bottom of the jointlocation were not heated by the hot plate, and thus they have actedcooperatively with the hinge pintle and gudgeon engagements to ensureachieving the desired joint/chamber configuration. Still other weldingmeans may be used; for instance, ultrasonic welding may be used to fusethe faying surfaces. Thus, in carrying out this aspect of the inventionthe faying surfaces become fused directly (as by the hot plate orultrasonic method) or indirectly (as by the use of the fusion weldelement) to each other.

While it may not ordinarily be necessary, the top portions of the halfchambers which are welded can be further secured to each other by usinga method selected from the group consisting of (i) screw fastening; (ii)latching; (iii) clamping with one or more C-shape cross section clamps;(iv) running a locking rod lengthwise through a plurality of matingstirrups, wherein each half chamber has a plurality of stirrups; andcombinations thereof.

The fusion weld element (which may be also referred to a fusion elementor weld element herein) used in the preferred embodiment of the methoddescribed above is a component which may be heated, such as by electricresistance heating or electromagnetic induction heating to inducemelting of the element and local plastic environment. As an example, thefusion weld element may be a commercial product known as PowerCoreWelding Rod (PowerCore International Ltd., Ottawa, Ontario, Canada). Seealso U.S. Pat. Nos. 5,407,514 and 5,407,520, the disclosures of whichare hereby incorporated by reference. An exemplary PowerCore brand rodis an about 3/16 inch diameter thermoplastic rod having integratedelectric resistance wires of very fine diameter. The ends of the rod runout of the joint/part at selected end points; and when the wirescomprising the rod are connected to an electric power source they risein temperature and heat the rod and surrounding plastic causing meltingand fusion. The fine wires remain a part of the finished joint. Thatportion of the fusion weld element which sticks from the end of thejoint is severed, as by chiseling, and discarded.

As another example, the fusion weld element may be the preform which ispart of the commercial Emabond electromagnetic welding system (EmabondSolutions Co., Norwood, N.J., U.S.) As described in Lamarca U.S. Pat.No. 7,984,738 (the disclosure of which is hereby incorporated byreference) the fusion weld element preform may be a structure comprisedof plastic and magnetic particles. When an energized high frequencyinduction coil is placed in proximity to the joint, the particles act assusceptors of electromagnetic radiation and resultant induced eddycurrents cause the element to become heated sufficiently to melt thepreform and adjacent plastic, thereby fusing the joint. The metalparticles remain within the fused plastic part.

While the article and methods of making have been described in thecontext of making a particularly large chamber, the principles andfeatures of the invention can be applied to (a) making other arch shapeor circular corrugated structures including pipe products; and (b)chambers which are not extraordinarily large and which can be whollyfabricated in a mold by means of single injection mold shot, instance achamber or other product with a living hinge top joint.

The invention, with explicit and implicit variations and advantages, hasbeen described and illustrated with respect to several embodiments.Those embodiments should be considered illustrative and not restrictive.Any use of words such as “preferred” and variations suggest a feature orcombination which is desirable but which is not necessarily mandatory.Thus embodiments lacking any such preferred feature or combination maybe within the scope of the claims which follow. Persons skilled in theart may make various changes in form and detail of the inventionembodiments which are described, without departing from the spirit andscope of the claimed invention. While, for simplicity and easing thedescription, the invention has been described in terms of being orientedwith the flanges on a horizontal plane, associated terms such as “top,”“bottom,” “base,” “side,” and the like should not be considered aslimiting when applied to a real article, since a chamber can be storedand shipped in a choice of different orientations.

What is claimed is:
 1. A method of fabricating a molded plastic chamberadapted for receiving water when buried beneath the surface of theearth, the chamber articulable from a transport configuration to a useconfiguration, the chamber comprising opposing side base flanges at achamber base, two opposing sidewalls, one each running from a baseflange to a chamber top, the chamber comprised of a first half chamberand a second half chamber connected to each other at a lengthwiserunning hinge joint at the top of the chamber; wherein in useconfiguration said chamber has a length, a height, a base and associatedbase plane, said chamber top, an arch shape cross section, a verticalcenter plane running lengthwise and intersecting the chamber top, saidtwo opposing corrugated sidewalls, each sidewall running upwardly fromone of the base flanges to the top of the chamber, wherein base flangesare spaced apart and wherein each base flange has an interior edge lyingin said base plane; and wherein in transport configuration the chamberhas a height which is substantially reduced and a spacing between thebase flanges which is substantially increased, compared respectively tothe chamber height and the base flange spacing which the chamber haswhen in use configuration; which method comprises: separately molding afirst half chamber and a second half chamber, each half chamber havinghinge features and at least one faying surface at the top portion of thehalf chamber; mating a first half chamber with a second half chamber toform a chamber, wherein the hinge features on the mated pair of halfchambers engage with each other as mutually rotatable features to formsaid hinge joint; rotating the half chambers about the hinge joint toplace the chamber in a configuration which is close to said useconfiguration and to position the at least one faying surface of thefirst half chamber into close proximity to the at least one fayingsurface of the second half chamber; interposing a fusion weld elementbetween said faying surfaced which are in close proximity; and, heatingat least a portion of each said at least one faying surface, by means ofsaid fusion weld element while contemporaneously applying upward forceproximate to said hinge joint, so that the force of gravity urges eachhalf chamber to rotate about the hinge joint, so that the fayingsurfaces move closer to each other.
 2. The method of claim 1 wherein thefirst half chamber and second half chamber are substantially identicalin configuration.
 3. The method of claim 1 wherein, following said stepof mating, a plurality of like-formed and like mated chambers areadditionally fabricated, wherein the plurality of chambers are stackedand transported while nested with each other when in transportconfiguration, and wherein, during said steps of rotating the halfchambers and heating each chamber is lifted and suspended verticallyfrom the stack by pulling upwardly at the top of the chamber proximateto said hinge joint.
 4. The method of claim 1 further comprising:further securing the top portion of the first half chamber to the topportion of a mated second half chamber, to furthermore keep the chamberin said use position, using a method selected from the group consistingof screw fastening, latching, clamping with one or more C-shape clamps,and the method of providing each half chamber with a plurality of matingstirrups and running a locking rod lengthwise through the plurality ofmating stirrups, and combinations thereof.
 5. The method of claim 1wherein the hinge features formed in said step of molding a half chambercomprise forming a plurality of integral pintles on the first chamberand forming a plurality of gudgeons on the second half chamber, thepintles and gudgeons respectively located nearer to the top of each halfchamber than is said at least one faying surface; and wherein said stepof mating further comprises translating lengthwise the first halfchamber relative to the second half chamber to engage the pintlefeatures with the gudgeon features.
 6. The method of claim 1 whereinduring said step of molding or said step of mating at least one fusionweld element that melts due to application of electric current is tackwelded to said at least one faying surface of at least one of said halfchambers.
 7. The method of claim 6 which further comprises flowingelectric current through the fusion weld element of the chamber for apredetermined time so that the degree of melting of said at least onefusion weld element allows the mated at least one faying surfaces tomove closer to one another by a predetermined amount.
 8. The method ofclaim 2 wherein said chamber is shaped at one end with a largercorrugation for overlapping or a smaller corrugation for beingoverlapped by the end of a like chamber.
 9. The method of claim 1further comprising, after said mating step and prior to said rotatingstep: stacking the multiplicity of chambers one upon the other to form anested stack of chambers wherein the chambers in said transportconfiguration; and, transporting the nested stack of chambers to a pointof assembly and removing chambers successively from the nested stack.